Boston's Isabella Stewart Gardner Museum is known for its vibrant art collection depicting renaissance scenes. But on the night of Saint Patrick's Day in 1990, robbers swept in, terrorizing the guards and taking 13 pieces of art which have never been recovered and are now worth half a billion dollars. This episode of How It Really Happened includes an interview with the museum security guard on duty who details the events of that night and his experience being held captive by the intruders, with never-before-seen museum security footage. FBI special agents, government officials and local journalists who covered the case provide expert insight into the international undercover operation attempting to recover the missing art and the key players in organized crime who have been suspected of the heist.